> People will start asking where your funds are coming from.

This is a weird statement.

If it's a cash offer, it's a seller's job to determine if you have the money, not if you paid taxes on it.

If it's a mortgage down payment, then the bank is more interested in if your assets are going to disappear (e.g. are they actually a loan from a third party?). I've never had a mortgage bank inquire about my tax situation.

If you're talking about IRS audits... then yes, they might be curious how you purchased a giant asset without any declared income. But that's similar to any unreported income situation.